Lithography processes are used to transfer patterns from a mask to a semiconductor device. As feature sizes on semiconductor devices decrease into the submicron range, there is a need for new lithography processes to pattern high-density semiconductor devices. Projection electron-beam lithography is a well-known reduction technique for patterning semiconductor devices. In general, a projection electron-beam lithography system scans a beam across a mask to create an image on the semiconductor device. Electron optics can be inserted to provide a means of image reduction. One particular type of projection e-beam lithography is known as Scattering with Angular Limitation in Projection Electron-Beam Lithography developed by Lucent Technologies, Incorporated of Murray Hill, N.J. The basic principles of this technique are illustrated in prior art FIG. 1.
From prior art FIG. 1, a mask 10 having a patterned scattering layer 14 is provided on membrane 12, through which an electron beam is projected, as represented by the flux arrows 13. The patterned scattering layer produces more electron scattering than the membrane 12 as a result of the difference in atomic numbers between the composition of the patterned scattering layer 14 and the membrane 12, i.e., the patterned scattering layer 14 has a higher atomic number than that of the membrane 12. The scattering effect 16 of the electron beam through portions of the mask 10 is illustrated in FIG. 1. As shown, those portions of the electron beam that pass through the patterned scattering layer 14 tend to be scattered through larger angles, as depicted by the scattering effect 16, when compared with those less scattered portions 17 that pass between unpatterned portions of the scattering layer 14.
As shown, the electron beam that passes through the mask 10 is focused through an electron focusing system represented by lens 20. The electron beam then passes through back focal plane filter 30 having an aperture 18 that is provided to permit passage of those portions of the electron beam that were not scattered by the patterned scattering layer 14 of the mask 10 through some finite angle. The electron beam is then projected onto a semiconductor wafer 40 having a plurality of die 42 and a resist layer 44 spun on the semiconductor wafer 40 by conventional techniques. The electron beam forms a high contrast image including areas of low intensity formed by those scattered portions 16 of the electron beam that pass through patterned portions of the mask 10, and areas of relatively high intensity formed by those unscattered portions 17 of the electron beam that pass through the unpatterned areas of the mask 10. In this way, a high-resolution image may be projected onto the resist layer 44, which is then developed to form an exposed resist layer. The patterned resist layer 44 may be used as an etch mask for the underlying material. It is noted that the electron optics of the system may be adjusted so as to provide a reduction in image size, typically 4.times. or one-fourth the image size on the mask 10.
Prior art FIG. 2 is a cross-sectional view of the membrane film 12 and patterned scattering layer 14 (grouped in dashed line 25), shown in FIG. 1, oriented onto a mask 26. In prior art FIG. 2, a silicon substrate 27 with a membrane film 12 on top of the silicon substrate 27 has been patterned to form two different struts, struts 29 (shown by dashed lines) and struts 31. The two types of struts are formed depending on the choice of orientation of the single crystal silicon substrate and are not present at the same time but are shown together here for exemplary purposes. The problem with the strut 29 is that the angle 32 at which the strut 29 contacts the membrane film 12 is at about 54 degrees which results in increased coverage of the membrane film 12. This, in turn, leaves less unobstructed membrane film 12 on which the patterned scattering layer 14 must be located between the struts. Further, the problem with the strut 31 is that due to the horizontally long and narrow shape of the strut 31, such a strut has a high aspect ratio which results in an unstable support structure for the membrane film 12.
A need therefore exists for forming a strut that takes up less surface area of the membrane film 14 while also providing a stable support mechanism for that membrane film.